1. Field of the Invention
The present invention relates generally to a wafer polishing apparatus, and more particularly to a wafer polishing apparatus which is used with a chemical mechanical polishing (CMP) method.
2. Description of Related Art
According to a conventional wafer polishing apparatus used with the CMP method, it is difficult to directly detect the stock removal of the wafer during polishing, and thus, the stock removal of the wafer is controlled by managing a polishing time. For this reason, a dummy wafer is polished at regular intervals to find the stock removal in accordance with the polishing time, and this stock removal is compared with a model stock removal as a basis. If the difference between them is within the permissible level, the polishing continues, and if the difference exceeds the permissible level, the polishing is stopped to dress or replace the polishing pad.
The wafer polishing apparatus disclosed in Japanese Patent Provisional Publication Nos. 6-79618 (corresponds to U.S. Pat. No. 5,205,082) and 8-229808 adheres the wafer to a carrier, and applies a pressure force to the carrier to press the wafer against the polishing pad, thus polishing the wafer.
According to another conventional wafer polishing apparatus used with the CMP method, the air is supplied into a space between the carrier and the wafer, and the wafer is polished while it is pressed against the polishing pad. Since it is difficult to directly detect the stock removal of the wafer, the sensor detects the movement amount of the carrier with the body of the wafer polishing apparatus being the basis, and the output of the sensor is regarded as the stock removal of the wafer. Thus, the stock removal of the wafer is detected indirectly.
The conventional wafer polishing apparatus, however, cannot correctly detect an end point (a target value) of the stock removal because the stock removal of the wafer is controlled by managing the polishing time.
Since the conventional wafer polishing apparatus polishes the dummy wafer to determine the timings for dressing and replacing the polishing pad, the yield of the wafer is deteriorated.
Moreover, since the normal polishing is stopped while the dummy wafer is polished, the throughput is lowered.
According to the polishing apparatus disclosed in Japanese Patent Provisional Publication Nos. 6-79618 and 8-229808, the carrier presses the wafer directly against the polishing pad. If there are some foreign matters such as polishing dust between the carrier and the wafer, the pressure force cannot transmit uniformly to the entire surface of the wafer, and the entire surface of the wafer cannot be polished uniformly.
According to the conventional wafer polishing apparatus which detects the stock removal of the wafer with the body of the wafer polishing apparatus being a basis, the body is expanded by heat which is generated during the polishing. For this reason, if the movement amount of the carrier is detected, the stock removal of the wafer cannot be detected correctly. Thus, the polishing end point of the wafer cannot be detected correctly.
The present invention has been developed under the above-described circumstances, and has as its object the provision of a wafer polishing apparatus which is able to automatically determine the timings for dressing and replacing a polishing pad during normal polishing, detect a polishing end point of the wafer correctly, and polish the entire surface of the wafer uniformly and detect the end point of the stock removal.
To achieve the above-mentioned object, the present invention is directed to the wafer polishing apparatus which presses a wafer against a rotating polishing pad to polish the surface of the wafer, the wafer polishing apparatus comprising: stock removal detecting means for detecting a stock removal of the wafer; storage means for containing a model stock removal of the wafer in accordance with a polishing time; control means for comparing the stock removal detected by the stock removal detecting means and the model stock removal stored in the storage means, determining timings for dressing and replacing said polishing pad in accordance with a different between the stock removals, and outputting determination results; and display means for showing the determination results output from the control means.
To achieve the above-mentioned object, the present invention is directed to the wafer polishing apparatus which presses a wafer against a rotating polishing pad to polish the surface of the wafer, the wafer polishing apparatus comprising: a carrier for holding the wafer; first pressing means for pressing the carrier against the polishing pad; pressure air layer forming means for forming a pressure air layer between the carrier and the wafer and transmitting a pressure force from the first pressing means to the wafer through the pressure air layer; a retainer ring which encloses the periphery of said wafer and holding the wafer; a polished surface adjustment ring for enclosing the periphery of said wafer, the polished surface adjustment ring as well as the wafer coming into contact with the polishing pad; second pressing means for pressing said retainer ring and the polished surface adjustment ring against the polishing pad; stock removal detecting means for detecting a stock removal of the wafer; and control means for outputting a polishing end signal when the stock removal detected by the stock removal detecting means reaches a preset target value.
To achieve the above-mentioned object, the present invention is directed to the wafer polishing apparatus which presses a wafer against a rotating polishing pad to polish the surface of the wafer, the wafer polishing apparatus comprising: a carrier for holding the wafer; pressing means for pressing the carrier against the polishing pad; pressure air layer forming means for forming a pressure air layer between the carrier and the wafer and transmitting a pressure force from the first pressing means to the wafer through the pressure air layer; a retainer ring provided outside the carrier and pressed against the polishing pad, the retainer ring preventing the wafer from jumping out from the carrier; a pressing member provided outside the retainer ring and pressed against the polishing pad; and stock removal detecting means provided at the pressing member and provided with a contact which comes into contact with a reverse side of the wafer pressed against the polishing pad through the pressure air layer, stock removal detecting means detecting a stock removal of the wafer in accordance with a movement amount of the contact.
To achieve the above-mentioned object, the present invention is directed to the wafer polishing apparatus which presses a wafer against a rotating polishing pad to polish the surface of the wafer, the wafer polishing apparatus comprising: a carrier for holding the wafer; pressing means for pressing the carrier against the polishing pad; pressure air layer forming means for forming a pressure air layer between the carrier and the wafer and transmitting a pressure force from the first pressing means to the wafer through the pressure air layer; a retainer ring provided outside the carrier and pressed against the polishing pad, the retainer ring preventing the wafer from jumping out from the carrier; a pressing member provided outside the retainer ring and pressed against the polishing pad; and stock removal detecting means provided at the pressing member and detecting a relative displacement of the pressing member and the carrier, the stock removal detecting means detecting a stock removal of the wafer in accordance with the relative displacement.
According to the present invention, the stock removal detecting means detects the stock removal of the wafer during the polishing, and the control means compares the stock removal detected by the stock removal detecting means and the model stock removal stored in the storage means. The control means determines the timings for dressing and replacing the polishing pad in accordance with a difference with the stock removals. The determination results are shown on the display means. This makes it possible to automatically determine the timings for dressing and replacing the polishing pad during the normal polishing. According to the pressure air layer forming means forms a pressure air layer between the carrier and the wafer, and the pressure force is transmitted from the first pressing means to the wafer through the pressure air layer to press the wafer against the polishing pad. If there is some foreign matters such as polishing dust between the carrier and the wafer, the pressure force can uniformly be transmitted from the first pressing means to the entire surface of the wafer. Thus, the entire surface of the wafer can be polished uniformly.
According to the present invention, there is provided the polished surface adjustment ring which comes into contact with the polishing pad with the wafer, and the second pressing means adjusts the pressure force of the polished surface adjustment ring which presses the polishing pad to thereby prevent the polishing pad from rising at the periphery of the wafer and make uniform the pressure which the polishing pad applies to the wafer.
According to the present invention, the stock removal detecting means detects the stock removal of the wafer during the polishing, and the control means outputs the polishing end signal to finish polishing when the stock removal detected by the stock removal detecting means reaches the preset target value. Thus, the end point of the stock removal can be detected correctly.
According to the present invention, the stock removal detecting means is provided at the pressing member which is pressed against the polishing pad with the wafer, and the contact of the stock removal detecting means comes into contact with the reverse side of the wafer to directly detect the stock removal of the wafer. Since the stock removal of the wafer is detected with the polishing pad being the basis, the polishing end point of the wafer can be detected correctly. In this case, the pressing member is prevented from being polished or deformed in order to serve as a position basis member (a zero point member) for the contact.
According to the present invention, the pressing member is arranged outside the retainer ring in order to prevent the wafer from colliding with the pressing member during the polishing. For this reason, the pressing member can be prevented from vibrating due to the collision with the wafer. Thus, the stock removal of the wafer can be detected correctly.
According to the invention, the stock removal detecting means is provided at the pressing member which is pressed against the polishing pad with the wafer, and the stock removal detecting means detects the relative displacement of the pressing member and the carrier to thereby detect the stock removal of the wafer. Since the stock removal of the wafer is detected with the polishing pad being the basis, the polishing end point of the wafer can be detected correctly.
According to the present invention, the stock removal detecting means is provided at such a position as to detect the stock removal at the center of the wafer. The vibration is the least at the center of the wafer during the polishing. According to the present invention which detects the stock removal at the center of the wafer, the stock removal of the wafer can be detected correctly.
According to the present invention, the stock removal detecting means is the differential transformer which is provided with the core and the bobbin. Thus, the stock removal of the wafer can be detected correctly.
According to the present invention, the stock removal detecting means is the light wave interference apparatus. Thus, the stock removal of the wafer can be detected correctly.
According to the present invention, the pressing member is made of material which is difficult to expand thermally, and the contact surface of the pressing member is coated with diamond or is made of ceramic. This prevents the pressing member from expanding thermally and being polished by the polishing pad during polishing. Since the stock removal detecting means attached to the pressing member detects the stock removal of the wafer with the polishing pad being the basis, the stock removal of the wafer can be detected correctly.
According to the present invention, the polished surface adjustment ring is arranged outside the retainer ring, and the polished surface adjustment ring is pressed against the polishing pad to flatten the polishing pad. The pressing member is pressed against the flattened polishing pad. This prevents the pressing member from vibrating vertically due to the unevenness of the polishing pad. The stock removal detecting means attached to the pressing member is able to correctly detect the stock removal of the wafer.